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Feline Heartworm Disease

By: Amanda Marcum, CVT

Let me start by saying cats do get heartworms. This statement is important, because for many years it was thought that cats were immune to the disease, or could spontaneously eradicate the worms from their system with no ill health effects. As veterinary medicine has advanced, so too has our understanding of feline heartworm disease and how it affects our feline companions.

Heartworm disease in cats begins with a mosquito. The mosquito first must bite an animal already infected with heartworms. During the feeding, the mosquito ingests microfilariae, or heartworm babies. The microfilariae mature into an infective larval stage, which can only take place within the mosquito. The mosquito then bites a cat, where it deposits these infective larvae. The larvae enter the body through the bite wound and migrate through the layers of tissue under the skin. After about four months, the larvae enter the bloodstream and travel to the pulmonary arteries, which are the main blood highways for the lungs. At this point, the cat’s immune system kicks in and attacks the larvae. This massive immune response causes marked inflammation within the structures of the lungs, which can lead to long term thickening of the air sacs and arteries. These cats may exhibit respiratory signs such as heavy breathing, wheezing, or coughing, signs that can sometimes be mistaken for asthma. This permanent respiratory damage is part of a syndrome called Heartworm Associated Respiratory Disease, or HARD.

Many, if not all of the larvae are killed during this initial immune response. Those that do survive will mature into adult worms three to four months later. These worms will live an average of two to three years in the cat, usually causing no ill effects during that period. However, when the worms die, they once again cause a massive immune response within the respiratory system, occasionally leading to sudden death.

Testing for heartworm disease is tricky in cats. Two blood tests, the antibody and antigen tests, are frequently used to help diagnose the disease, but the results can be vague. Radiographs and chest ultrasounds may help diagnose the structural changes associated with the disease, but usually will not show if the animal is currently infected.

Unlike dogs, treatment options are very limited in cats. There is currently no safe way to eradicate adult worms from an infected cat. The treatment method most often utilized is to allow the worms to die naturally while monitoring the cat for adverse effects, and providing medical care when needed.

The best way to avoid feline heartworm disease is through prevention. There are currently four products approved for the prevention of feline heartworm disease. Of these products, our preferred choice is Feline Revolution, a monthly topical application that prevents heartworms, kills fleas, and treats the two most common intestinal parasites. Using Feline Revolution will help ensure that your cat will live a long and healthy life, free of heartworms and dangers associated with the disease.